1. The Field of the Invention
The present invention refers to an actuator device with stable working positions.
2. The Relevant Technology
As is known, in order to control some components of apparatuses in general, such as household appliances, automatisms, vehicles, conditioners and the like, whose the operation is controlled either remotely (by means of control units or remote controls) or manually, actuators are used which may be of various kinds: electromechanical, thermoelectric, magnetic, hydraulic, etc.
Some of these actuators are cylinder-piston systems, wherein a movable part (either the cylinder or the piston, as the case may be) moves linearly and exerts a force on a mechanical member to be controlled.
The latter may be of any kind, shape and size, e.g., the door that closes a container, the gate of a valve, the flap of a ventilation system, and so on.
In this description and in the appended claims, reference will prevalently be made, for simplicity, to thermal or electrothermal actuators, or thermoactuators, which will be briefly discussed later on, it being understood that the invention is also applicable to other actuator types, since it is compatible therewith.
In the light of this introduction, the present invention can be said to relate, from a more particular point of view, to actuator devices with stable working positions, the latter being positions taken in specific conditions such as, for example, those for closing or opening doors, flaps and the like, as mentioned above, and/or positions held in the absence of thermal excitation and/or electric power.
In order to keep these stable conditions, abutment elements are usually employed, i.e., elements such as protrusions, shoulders or strikers, which stop the travel of the movable part of the actuator.
In such condition, the latter is kept operational by power supplied thereto or otherwise, so that it can exert the force necessary for controlling the member with which it is associated.
One example of a known actuator device designed as explained so far is described in American patent U.S. Pat. No. 7,063,092, the holder of which is the same Applicant of the present application.
This device uses a per se known monostable thermoactuator or thermoelectric actuator, such as an actuator with a metallic body, comprising a wax or another heat-expandable material, and a slidably inserted movable shaft or piston, which is moved by the wax expanding when heated by an electric resistor, subject to the elastic reaction of a spring for repositioning the movable shaft or piston when the electric supply or excitation stops.
A rack is associated with said known monostable thermoelectric actuator, which engages with a pinion whose rotations, imparted by the alternating linear motion of the rack, are used for opening and closing the door of a washing agent dispenser of a household appliance, such as a dishwasher or the like.
In particular, the dispenser opens at the end of the forward stroke of the thermoactuator's piston, and this condition is maintained for a preset time interval, so as to allow the wash water of the dishwasher to clean the dispenser compartment of all residues of the agents contained therein.
During this time interval, the thermoactuator or thermoelectric actuator is electrically powered to exert the force required for holding the dispenser open, and only at the end of this interval it is de-energized in order to close the dispenser.
As can be easily understood, such a solution, though efficient in opening and closing the dispenser, is not equally efficient from the energetic viewpoint, in that the thermoelectric actuator continues to draw electric current throughout the actuation time, i.e., as long as it is held in a second position other than a first idle position.
This may not be satisfactory because, as is the case of the latest household appliances, for example, very restrictive conditions must be complied with as far as energy consumption is concerned; the same applies to the case wherein a great force must be exerted on the member controlled by the actuator, since the large amount of power required by the actuator for long periods of time may turn out to be costly and/or harmful, resulting in the risk of premature failure of the actuator itself.
Let us consider, in fact, that the internal pressure of some thermoactuator versions may be as high as some hundreds of bar, or even in excess of 1,000 bar, resulting in the structure being subject to high mechanical stresses further increased by concurrent thermal stresses, which may vary depending on the actuator's heating or energization time.